The present invention relates to a solid-state image sensing device, and more particularly to an image sensor provided with an amplification or impedance conversion function for each pixel (picture element).
Conventionally, an image sensor provided with an amplification or impedance conversion function for each pixel has existed as a contact image sensor. This is because the manufacturing process thereof is relatively simple and additionally to output integrating method is simple when integrated as a multichip, when compared with image sensors having other structures (e.g. OCD sensor).
In the conventional image sensors as described above, a plurality of (N.gtoreq.2) of photodiodes are formed on a single chip, for instance, and there are arranged thereon source follower buffer circuits, reset gates, select gates, a shift register composed of (N+1)-piece transfer stages of roughly the same structure, and a common output line.
In the above-mentioned conventional image sensor, the respective transfer stages (i=1, 2, . . . N+1) of the shift register are driven in response to two different-phase drive pulses .phi..sub.1 and .phi..sub.2. However, since a control pulse inputted to the first transfer stage of the shift register is supplied externally and control pulses inputted to the second and after transfer stages of the shift register are formed internally on the basis of the drive pulses .phi..sub.1 and .phi..sub.2, the control pulse applied to the first stage does not necessarily match the waveform of the control pulses applied to the second and after stages of the shift register, in general.
In the case where both the control pulses do not match the waveform of each other, a read pulse generated by the first transfer stage of the shift register is slightly different in waveform from those generated by the second and after transfer stages (i=2, . . . N+1) thereof, with the result that the output waveform (e.g. pulse rise time and fall time) of the first pixel is different from the output waveforms of the second and after pixels under the influence of these read pulses, in spite of the fact that output signals of the same waveform must be generated properly. Therefore, when data are sampled at a constant timing, the output waveform from the first pixel differs in waveform from those from the other pixels without generating uniform waveform output, thus resulting in a problem in that the S/N ratio of the image sensor is deteriorated.